import {Pos} from "../line/pos.js"
import {prepareMeasureForLine, measureCharPrepared, wrappedLineExtentChar} from "../measurement/position_measurement.js"
import {getBidiPartAt, getOrder} from "../util/bidi.js"
import {findFirst, lst, skipExtendingChars} from "../util/misc.js"

function moveCharLogically(line, ch, dir) {
    let target = skipExtendingChars(line.text, ch + dir, dir)
    return target < 0 || target > line.text.length ? null : target
}

export function moveLogically(line, start, dir) {
    let ch = moveCharLogically(line, start.ch, dir)
    return ch == null ? null : new Pos(start.line, ch, dir < 0 ? "after" : "before")
}

export function endOfLine(visually, cm, lineObj, lineNo, dir) {
    if (visually) {
        if (cm.doc.direction == "rtl") dir = -dir
        let order = getOrder(lineObj, cm.doc.direction)
        if (order) {
            let part = dir < 0 ? lst(order) : order[0]
            let moveInStorageOrder = (dir < 0) == (part.level == 1)
            let sticky = moveInStorageOrder ? "after" : "before"
            let ch
            // With a wrapped rtl chunk (possibly spanning multiple bidi parts),
            // it could be that the last bidi part is not on the last visual line,
            // since visual lines contain content order-consecutive chunks.
            // Thus, in rtl, we are looking for the first (content-order) character
            // in the rtl chunk that is on the last line (that is, the same line
            // as the last (content-order) character).
            if (part.level > 0 || cm.doc.direction == "rtl") {
                let prep = prepareMeasureForLine(cm, lineObj)
                ch = dir < 0 ? lineObj.text.length - 1 : 0
                let targetTop = measureCharPrepared(cm, prep, ch).top
                ch = findFirst(ch => measureCharPrepared(cm, prep, ch).top == targetTop, (dir < 0) == (part.level == 1) ? part.from : part.to - 1, ch)
                if (sticky == "before") ch = moveCharLogically(lineObj, ch, 1)
            } else ch = dir < 0 ? part.to : part.from
            return new Pos(lineNo, ch, sticky)
        }
    }
    return new Pos(lineNo, dir < 0 ? lineObj.text.length : 0, dir < 0 ? "before" : "after")
}

export function moveVisually(cm, line, start, dir) {
    let bidi = getOrder(line, cm.doc.direction)
    if (!bidi) return moveLogically(line, start, dir)
    if (start.ch >= line.text.length) {
        start.ch = line.text.length
        start.sticky = "before"
    } else if (start.ch <= 0) {
        start.ch = 0
        start.sticky = "after"
    }
    let partPos = getBidiPartAt(bidi, start.ch, start.sticky), part = bidi[partPos]
    if (cm.doc.direction == "ltr" && part.level % 2 == 0 && (dir > 0 ? part.to > start.ch : part.from < start.ch)) {
        // Case 1: We move within an ltr part in an ltr editor. Even with wrapped lines,
        // nothing interesting happens.
        return moveLogically(line, start, dir)
    }

    let mv = (pos, dir) => moveCharLogically(line, pos instanceof Pos ? pos.ch : pos, dir)
    let prep
    let getWrappedLineExtent = ch => {
        if (!cm.options.lineWrapping) return {begin: 0, end: line.text.length}
        prep = prep || prepareMeasureForLine(cm, line)
        return wrappedLineExtentChar(cm, line, prep, ch)
    }
    let wrappedLineExtent = getWrappedLineExtent(start.sticky == "before" ? mv(start, -1) : start.ch)

    if (cm.doc.direction == "rtl" || part.level == 1) {
        let moveInStorageOrder = (part.level == 1) == (dir < 0)
        let ch = mv(start, moveInStorageOrder ? 1 : -1)
        if (ch != null && (!moveInStorageOrder ? ch >= part.from && ch >= wrappedLineExtent.begin : ch <= part.to && ch <= wrappedLineExtent.end)) {
            // Case 2: We move within an rtl part or in an rtl editor on the same visual line
            let sticky = moveInStorageOrder ? "before" : "after"
            return new Pos(start.line, ch, sticky)
        }
    }

    // Case 3: Could not move within this bidi part in this visual line, so leave
    // the current bidi part

    let searchInVisualLine = (partPos, dir, wrappedLineExtent) => {
        let getRes = (ch, moveInStorageOrder) => moveInStorageOrder
            ? new Pos(start.line, mv(ch, 1), "before")
            : new Pos(start.line, ch, "after")

        for (; partPos >= 0 && partPos < bidi.length; partPos += dir) {
            let part = bidi[partPos]
            let moveInStorageOrder = (dir > 0) == (part.level != 1)
            let ch = moveInStorageOrder ? wrappedLineExtent.begin : mv(wrappedLineExtent.end, -1)
            if (part.from <= ch && ch < part.to) return getRes(ch, moveInStorageOrder)
            ch = moveInStorageOrder ? part.from : mv(part.to, -1)
            if (wrappedLineExtent.begin <= ch && ch < wrappedLineExtent.end) return getRes(ch, moveInStorageOrder)
        }
    }

    // Case 3a: Look for other bidi parts on the same visual line
    let res = searchInVisualLine(partPos + dir, dir, wrappedLineExtent)
    if (res) return res

    // Case 3b: Look for other bidi parts on the next visual line
    let nextCh = dir > 0 ? wrappedLineExtent.end : mv(wrappedLineExtent.begin, -1)
    if (nextCh != null && !(dir > 0 && nextCh == line.text.length)) {
        res = searchInVisualLine(dir > 0 ? 0 : bidi.length - 1, dir, getWrappedLineExtent(nextCh))
        if (res) return res
    }

    // Case 4: Nowhere to move
    return null
}
